Despite Rick Riordan's best intentions, there are mistakes in the Percy Jackson and the Olympians series and The Heroes of Olympus series, either based on continuity or character flaws. While some of these have explanations, even coming from Rick Riordan himself on his blog or Twitter, not all are explained directly in the books and can still be considered mistakes. There are also other errors in the series that may never be explained and can only be considered mistakes.

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Sally Jackson says that Poseidon was only with her for the summer. However, it is mentioned that Percy's birthday is August 18th, which is during the summer. This would mean that Poseidon and Sally would have to have been together around December for Percy to be born in August.

When talking to Grover, Grover says that he may be a son of Nemesis, but Nemesis is a female goddess.

This could just be poor wording, as Grover says Percy may be a child of "one of the minor gods, like Nemesis, the god of revenge." This could mean that Grover was using Nemesis as an example of a minor god and not implying she was his father.

When talking to Luke about Hermes, Luke mentions that some of the things that Hermes represents are "Messengers. Medicine. Travelers," though Hermes is not the god of medicine, Apollo is. He might have said that because Hermes' staff is a symbol of hospitals.

Luke claims to have only seen Hermes once in his life (when he was 14). However, since Luke attended the campers field trip to Mount Olympus during the Winter Solstice (during which all of the Olympians must be present), he should have seen Hermes there as well.

It is possible that despite chaperoning the trip, Luke never went into the throne room with everyone else.

Chiron claims that the Titans are still alive but imprisoned. This seems to be supported by Poseidon telling Percy that the Titans cannot die anymore than the gods can. However, their claims are contradicted in House of Hades when Krios says that Jason Grace killed him.

Percy speaks in Latin, although Greek demigods should speak in Greek and not Latin.

This may be because the Roman demigods were not planned by Rick at this time.

Before Ares decides to battle Percy himself, he sends a fierce wild boar to attack him. Percy notes that the boar is "even larger and uglier than the one whose head hung above the door on cabin seven". However cabin seven is Apollo's, Ares' cabin is cabin five.

It is physically impossible to fall from the Gateway Arch in St. Louis into the Mississippi River, as the Gateway Arch does not span the river. It is in fact almost five hundred feet from the edge of the Mississippi River normally. Falling straight down would land him in the middle of the grassy park of the Jefferson National Expansion Memorial.

While riding in the Gray Sisters' Taxi, Tempest constantly asks for the eye from Wasp despite Anger being the one with the eye. However, even though Anger had the eye, Wasp managed to warn Tempest to move before crashing the taxi.

It is possible that because Tempest didn't have the eye, she couldn't see which of her sisters had the eye at the time. How Wasp managed to warn Tempest without the eye before they crashed is unknown.

On page 131, Oreius is spelled "Orieus," but in the rest of the book, his name was spelled "Oreius."

This is a typo.

Thalia Grace appears in Percy's dreams during the story. In his dreams, she is described as having stormy green eyes. However, when she is revived and appears in later stories, her eyes are said to be electric blue.

When asked this question by his fans, Rick Riordan admitted that this was an error on his part.

Annabeth Chase tells Percy that she knows parts of the Great Prophecy, but not the complete prophecy. Later in the series, she mentions knowing the prophecy in its entirety and that it still gives her nightmares.

She may have learned the full prophecy later in the series. However in The Last Olympian, she says she read it when she was ten years old and she was thirteen in The Sea of Monsters.

She might have forgotten some portions of the prophecy after 3 years. Though this is unlikely since in The Battle of the Labyrinth, Percy states that Annabeth "never forgot something she heard."

She could've also been lying to avoid being questioned any further.

While saving Blackjack from the Princess Andromeda, Percy calls Blackjack a mare (a female horse). However Blackjack is a male in all other appearances.

During a Q&A on Rick Riordan's Twitter account, he stated that Percy didn't know Blackjack was male at the time. This mistake is never addressed by Percy or Blackjack in the series however.

Annabeth tells the story of the Golden Fleece using the names Cadmus and Europa when it should have been Phrixus and Helle. Considering Annabeth's vast knowledge of Greek mythology, such a big error is surprising.

Hades is not at the Winter Solstice meeting on Olympus, even though this is the only time he is allowed on Olympus and has to attend the meeting.

This could simply mean Percy did not see him, although he is not mentioned having voted either.

Percy inquires whether or not it would be possible to contact a god via Iris Message. He had already done this when he contacted Dionysus while aboard the Princess Andromeda in The Sea of Monsters.

When Ares curses Percy's sword in The Lightning Thief, he says "Every time you raise your blade in battle, every time you hope for success, you will feel my curse. Beware, Perseus Jackson!" However when the curse is activated, Percy remembers it as "When you need it most, your sword will fail you."

Percy might not recall the exact words of Ares' curse.

Also the curse only takes hold during his fight with Atlas, despite Percy using his sword in other battles with no ill effects. It is possible that Ares meant that his curse could take hold at any time and to remember that every time he went into battle.

The prophecy Zoe is given does not rhyme. The first line ends in chains, and the second line ends with rain.

While Percy is Iris-Messaging his mother and Paul, he mentions that the light from the bathrooms made a faint rainbow. However, in the first book, Percy says that there are bathrooms in a cinderblock building.

This could be because of the Patrol Harpies, who make sure that the campers would not go out at night.

Thalia states that the apples of immortality were a wedding gift to Hera from Zeus, when in fact, they were given by Gaea (as seen in Percy Jackson's Greek Gods).

It is possible that because Silena is a daughter of Aphrodite, her hair and eye color can change naturally like Aphrodite, though it is never mentioned to be an actual power for her demigod children.

Hestia, when speaking with Nico and Percy outiside May Castellan's house, agrees with Percy that she gave up her seat for Dionysus. However, in Percy Jackson's Greek Gods, Percy says that Hestia didn't even take a seat in the Olympian Council.

On page 175, there's this sentence: “Shh,” Annabeth. “Hello, William.” The word "said" does not follow after Annabeth like it should.

This is a misprint.

On page 176, Percy say's this to Annabeth: "I’ll all invincible and stuff.” He says "I'll" instead of "I'm."

This is a misprint.

At the end of chapter 11, when Percy gets a call from Silena about Annabeth after she got stabbed, Percy mentions the Caller ID on his mother's cell phone to be from Finklestein & Associates, but cell phones don't have Caller ID like landlines do, even to this day. On cell phones, when someone calls you, it only shows the number, never the name of the person calling unless it's listed on your contacts.

It's possible that Percy's mom has that number listed on her contacts.

It is revealed that after Zeus had tried to kill Bianca and Nico di Angelo, Hades had the two placed in the Lotus Hotel and Casino, giving him the possibility to use them to control the Great Prophecy, as the demigods would not age once inside. However they were placed inside when they were very small kids, so it is unknown how they grew to the ages they are at in The Titan's Curse.

When Percy Jackson starts fighting the Clazmonian Sow, he correctly calls it "her." However when Percy is giving Blackjack instructions further on in the fight against the sow, he says "Get in front of the pig. Taunt him!"

Percy might have been panicking and regarded it wrong.

Connor Stoll's name is spelled 'Conner' whereas in the rest of the series it's been spelled 'Connor'.

This is a typo.

After Silena Beauregard's death, on page 296 of the American paperback, Annabeth says; "We have to fight." Then, on page 302, it says: (Quote) ' "Percy." Annabeth said quietly. "You were right about Luke." It was the first time she'd spoken since Silena Beauregard's death. ' (End quote)

When Hestia is showing Percy a flashback of when May Castellan is trying to inherit the spirit of Delphi, he says it is Camp Half-Blood in a different generation, the 1990's. However, during this period, Luke Castellan is a baby, born in 1986, meaning the year was either 1986 or 1987.

This could just be Percy's misinterpretation of the era, and a rough guess on his part.

After Annabeth lets Piper use her cell phone, she looks on the Caller ID of the number that Piper dialed and it had her last name on it, but cell phones don't have Caller ID, and even if they did, they don't show you the Caller ID of the number you're dialing unless that number is listed on your contacts.

While Jason Grace is given a tour of Camp Half-Blood, it is said that all the new cabins were built last year. However The Lost Hero takes place only four months after The Last Olympian.

This may be because it is a new year.

During the fight on Mt Diablo, Enceladus mentions that Jason had killed the Titan Krios. This is contradictory to what Hermes told Percy, that Titans cannot be killed. It can be inferred that Jason had defeated and badly Injured the Titan.

Porphyrion is misspelled as "Porphryion" and Tartarus is also misspelled as “Tatarus” on page 508.

Enceladus claimed to be the shortest and smallest Giant of all, being "only" 30 feet tall. However in The Son of Neptune, Polybotes is no taller and in The House of Hades, Damasen and Clytius are both shorter, being only 20 feet tall. In The Mark of Athena, Otis and Ephialtes are only 12 feet tall. Even their combined height is still considerably shorter than Enceladus's. Still, the shortest Giant of all is, in fact, Orion, who is short enough to be mistaken for a human.

When Jason's memories return, he mentions Hazel as a good friend of his. However in The House of Hades, Hazel admits that she has a hard time warming up to him, and that she can't get a read on him. Overall, Jason seems to be more of a legend to her than an actual person, and she would rather be accompanied by Frank, Nico, Piper or Leo than Jason. This implies that the two barely knew each other before Jason disappears. (He may have considered her a friend while she didn't return the feeling)

In the gods section in The Lost Hero, Aphrodite is said to be 'marred' to Hephaestus. 'Marred' means to inflict serious damage, so the correct word should have been 'married'.

Hera/Juno told Jason that gods never experience of having a dream that it is contrary on Ares' (somehow) confession that he is having dreams about 'someone' who whispered him words that will break his family apart.

Thanatos tells Frank after the giant is unconscious that they will meet again in unfavorable circumstances. However, this meeting does not occur at all, even until the end of the series.

Percy yells at Hera for taking eight months of his life from him. However Percy was only gone for six months, as he vanished from Camp Half-Blood on December 13 and then appeared at Camp Jupiter in late June.

Percy might have thought that he was gone that long, because Jason went missing from the Roman Camp in October, eight months before the book's events. He eventually realized his error in The Mark of Athena.

Percy is being chased by Stheno and Euryale, the Gorgon sisters of Medusa. Meanwhile in The Lightning Thief, Medusa mentions to Percy that her sisters had faded (which is the equivalent of permanently dying for immortals and monsters) after being forgotten in her shadow.

However Euryale says that Gaea brought them back, so there is a possibility that Gaea's powers include bringing back monsters after they fade. Or, they could of returned via the Doors of Death, which is the reason why they never stayed dead very long.

Medusa says her sisters have "passed on," meaning that they may not have faded and were only reforming at the time of The Lightning Thief.

In some editions of the book, Julia's name is once misspelled as "Juila."[1]

Hazel is told by Pluto that her curse would be washed off by a descendant of Neptune. However, further details about who washed it off, how, where, when, etc., are not mentioned even until the last book.

On some hardcover editions, there is a typo on the back cover, misspelling "Heroes of Olympus" as "Heroes of Oympus."

Thalia said that Amaltheia led her to find Luke the night that she ran away. But Thalia said that she ran away when Jason disappeared when he was two, and since she was seven when he was born, that would've made her nine-years-old, but Thalia and Luke only knew each other a few months before they met Annabeth, and they were 12 and 14-years-old.

Soon after the Argo II arrives at Camp Jupiter, it is mentioned that Hylla had left earlier in the morning. However Hylla was present in the Senate meeting when the Argo II first arrived at the camp.

Hylla might have left right afterwards.

Soon after the Argo II is forced to flee from Camp Jupiter, Percy sees the sun set over a live feed of Camp Half-Blood. However at the time, it was early afternoon at Camp Jupiter and with only a four hour difference between camps, it is unlikely that it was a sunset.

Hazel Levesque mentions to Leo that she had not had a flashback in a long time. However she only refrained from having a flashback for a few days at this point. Even during The Son of Neptune when they were supposedly at their worst, she still only had one a day at most.

Hazel may have ADHD, making it seem longer. This is unconfirmed however, as children in the 1940s with ADHD would have been called lazy instead.

Alcyoneus states in The Son of Neptune that he must rise before any of his fellow Gigantes, as he is the oldest. However Otis and Ephialtes have been helping Arachne capture demigods for centuries.

It is possible that Otis and Ephialtes never truly rose, as they made a home under the surface of Rome.

Piper and Jason meet Hercules, who tells them that he is more often known as Hercules.

Percy mentions that he knew the Romans for weeks. However by this point in the series he had only known the Romans for about ten days, including the time he spent with Frank and Hazel on his quest.

Hercules warns Piper and Jason that he will kill them and their friends on the Argo II if they try and contact them. Later when Piper thinks of a plan to pass Hercules without giving him the Cornucopia, she uses an Iris Message to contact them.

It is possible that Hercules simply got distracted and didn't notice the message.

Frank Zhang mentions in The Son of Neptune that the only Chinese character he knows is his family name. However in The Mark of Athena, he is able to read enough Chinese to find a location marked on a map by a Chinese tourist.

Percy mentions that it has been five years since he arrived at Camp Half-Blood. However The Mark of Athena only takes place four years after the events of The Lightning Thief.

Percy claims that Chrysaor is just as good of a swordsman as Ares himself. However since Percy was able to defeat the god of war in a sword fight and has increased in power since then, it is unlikely that Chrysaor would have been able to defeat him so easily.

Though it might be because Ares' going easy on Percy.

Leo comments on the discovery of the Archimedes sphere, saying that it is bigger than Daedalus' laptop. However it is spelled "Daedlus's."

Rick explained on his Twitter that calling Octavian a son of Apollo is honorific, and compared it to calling mankind "sons of Adam," when they are actually descendants of him.

Leo Valdez yells at Gaea that she lied to him about his great grandfather having died in the 1960s. Actually she lied to Hazel, not Leo.

At the start of chapter 2, Hazel compares the joy of seeing Arion to her first kiss with Frank Zhang, which in her thoughts happened after the battle of New Rome. However in The Son of Neptune, they first kiss up in Alaska after Frank kills the giant.

However they might have kissed again after the battle and Hazel considers it to be the "first" kiss of their relationship, since Frank was initially uneasy during their first actual kiss.

Bianca's perception of time within the casino might have been different from Nico's.

It is said that Leo's army jacket burned up. However in The Lost Hero when Aphrodite gives them a makeover before they battle Enceladus, she takes his army jacket and swaps it for a dress shirt, suspenders, and trousers.

It is possible he mixed up the names, as his Greek and Roman sides were both struggling for control at the time inside of Frank's head.

Nico bitterly says that since he is a son of Hades, he has no friends and "might as well be covered in blood or sewage," judging from how almost all other demigods fear and hate him. However in The Last Olympian after Nico helps save Olympus, Percy states that everybody acted friendly with him and complimented his amazing fighting skills. Even the Ares demigods consider him "pretty cool."

However, Nico could be using this as cover for his overwhelming fear of coming out of the closet.

Krios claims that Jason Grace killed him on Mt. Othrys. However, this contradicts Chiron's claim in Lightning Thief that the Titans are alive but imprisoned and Poseidon telling Percy that the Titans cannot die anymore than the gods can.

Jason cannot recall the story of Calypso when he realizes that was where Leo had disappeared to, believing her to be an evil sorceress. Yet according to Leo, Piper had told Jason about Percy's time with Calypso after she had heard it from Annabeth.

Based on the nature of the book being about Percy recounting certain myths and adding "his own magic--and sarcastic asides--to the classics," certain information from the book may contradict with information from the main series of stories. As a result, if something is mentioned in this book that is mentioned differently in the series, please add it below.

When Chiron reminds Percy of Poseidon and Hera's unsuccessful Olympian riot against Zeus (which was addressed in question 38 of his final exam), Percy recalls that Zeus was trapped in a golden net. However, in Percy Jackson's Greek Gods, it is revealed to have been a magical rope instead.

This could have been Rick Riordan showing how basic Percy's knowledge of mythology was.

When Chiron corrects Percy's mistakes about Kronos and the Titanomachy, he mentions that the extremely powerful emetic Zeus gave Kronos was "a mixture of mustard and wine," while in Percy Jackson's Greek Gods, it is actually revealed to have been a mixture of mustard and nectar. In any case, Zeus could not have used wine, since that particular beverage was invented by his son Dionysus, many years after the Titanomachy.

The Telekhines claim to have been the ones to forge Poseidon's mighty Trident. However, in Percy Jackson's Greek Gods, the Trident is shown to have been made by the Elder Cyclopes.

Tyson claims that Briares, as a Hekatonkheire giant, is older than Cyclopes. However in Percy Jackson's Greek Gods, the three Hekatonkheires are stated to have been born to Gaea and Ouranos after the Elder Cyclopes.

Hephaestus claims that Hera hurled him from Mount Olympus instead of Zeus. However, as revealed in Percy Jackson's Greek Gods, Hephaestus was hurled from Olympus twice: first by Hera, and then by Zeus.

Demeter is described as having black hair. However in Percy Jackson's Greek Gods, she is described as blonde.

Demeter is a goddess, meaning she can change her physical appearance.

Hermes mentions that the Olympians fought Typhon all together for the first time. However in Percy Jackson's Greek Gods, it is revealed that Zeus was forced to fight the Storm Giant one-on-one, and finally prevailed.

In The Last Olympian, Krios' armor was described as being black, while Percy Jackson's Greek Gods claims that it was "navy blue."

Also In the House Of Hades, Percy mentions seeing the "navy blue" armor.

When Hestia and Percy talk, she claims that she gave her throne to Dionysus to prevent a war among the gods. This is odd considering that in Percy Jackson's Greek Gods, Hestia was too modest to accept having a throne in the first place.

Hera mentions that she and Zeus only have two children (Ares, and Hephaestus). However in Percy Jackson's Greek Gods, Hera and Zeus are mentioned to also have Hebe (the goddess of youth), Enyo (the goddess of war), and Eileithyia (the goddess of childbirth) as daughters.

It's possible Hera was simply referring to having only two children of her own on the Olympian Council or possibly only talking about her sons.